Process of treating furnace-slag.



urrn

'rarns PATENT OFFICE.

PROCESS OF TREATING FURNACE-SLAG.

SPECIFICATION forming part of Letters Patent No. 669,019, dated February26, 1901.

Application filed January 9, 1900. Serial No. 874. (No specimens.)

To all whom, it may concern:

Beit known that I, SAMUEL W. VAUGHEN, a citizen of the United States,and a resident of Johnstown,in the county of Cambria and State ofPennsylvania, haveinvented a certain new and useful Improvement inProcesses for Treating Furnace-Slag; and I do declare the following tobe a full, clear, and exact description of the invention, such as willenable others skilled in the art to which it appertains to make and usethe same.

This invention relates to the utilization of the hitherto waste slagmade by blast-furnaces producing pig-iron and also other furnaces ofsimilar character. This waste material has been in the past generallythrown away, and the disposing of it has been a source of expense to themanufacturers.

The invention consists in the process for the recovery of the silica,lime, magnesia, alumina, &c., contained in furnace slags, hereinafterset forth.

Slag consists principally of lime and magnesia combined with silica,containing also considerable quantities of alumina and lesser amounts ofiron and manganese. On account of the manner in which these elements arecombined as silicates it has been heretofore found impracticable toseparate them or bring them into any useful forms except by somegrinding processes which do not change their chemical form. It was notgenerally believed to be a commercial success to treat the slag withacids, for the reason that too much of the acid would be absorbed by thelarge amount of lime presentin the slag; but I have devised a method bywhich the acid absorbed is recovered as a valuable product, based on mydiscovery that the lime sulfate produced in treating blast-furnace slagwith sulfuric acid may be by certain methods of treatment made into amaterial which has all the properties of plaster-of-paris, which is, infact, impure plaster-of-paris and very suitable as a basis for themanufacture of wall-plaster and other similar purposes.

Hy new and improved process is as follows: The liquid slag as it flowsfrom the blast-furnace is granulated by being run into large vesselsfilled with water. This sandy material is next introduced into agrinding-mill,

and to the mass is added sulfuric acid in regulated quantity, and thewhole is then ground together until the lime and the sulfuric acid reacttogether, forming lime sulfate and separating out the silica. When thereaction is over, the Whole contents of the mill is transferred to adrying-plate and dried until any gelatinous silica becomes dehydrated.The dry material is next run through a dry grinding-mill and into a wetbur-mill, into whicha small quantity of Water is added. This leaches outall of the sulfates which are soluble in water, and the whole mass ofsoluble and insoluble sulfates and silica is next run through afilter-press and the insoluble lime sulfate mixed with silica separatedfrom the soluble portions. This mixture of lime sulfate and silica Ihave discovered can be transformed into a material which I call whiteresidue, having all the properties of plaster-of-paris. This is donebysubjecting it to a calcination at a proper temperature in a similarmanner to that practiced in the manufacture of plaster-of-paris fromnatural gypsum-rock. In the use of Wallplaster made in the ordinary waysand or silica is added either at the time of applying to the Wall orpreviously in the course of the manufacture. When using my whiteresidue, however, for such purposes, a less quantity of sand has to beadded, for the reason that it already has a certain amount of thisingredient present.

As blast-furnace slags vary somewhat in the proportion of silica andlime which they carry, I find it convenient before dissolving to add, ifnecessary, a small amount of lime or limestone to the mixture in suchquantities as will bring up the total percentage of lime to aconstantthat is, where a slag is too high in silica and low in lime Iadd enough lime (usually from five to twentyfive per cent. of the slagweight) to equalize it before dissolving. In practice, therefore,

before mixing the slag and the acid I first subject the slag to acomplete chemical analysis, and if I find that the particular sample tobe treated is too low in lime-that is, if it is found to be belowforty-five per cent. of limeI add enough lime to it to bring up thetotal percentage of lime to forty-five per cent, or thereabout. I thenproceed, as above described. to separate and recover the differentelements of the slag. After the insoluble lime sulfate mixed with silicahas been separated, as above described, in the filter-press from theliquor containing the balance of the elements-viz, the alumina sulfate,iron sulfate, magnesia sulfate, and

manganese sulfateI proceed to recover the latter substances in thefollowing way: I concentrate the liquor to a consistency of about 20Baum, when I find that a part of the magnesia sulfate unites with someremaining lime sulfate and forms fiat crystals of a donble-lime-magnesiasalt, which I separate out and find to be a useful product for thepurposes, of covering steam-pipes, deadening walls, &c., and also as abasis for the preparation of other magnesia salts. The liquor is againconcentrated by means of heat and enough sulfate or chlorid of potassiumadded to crystallize out about three-quarters of the amount of aluminapresent in the liquor in the form of potash alum. Any potash saltissuitable for this purpose. After allowing this strong liquor to standfor some time I find that about three-quarters of the alumina hasseparated out in the form of crystals of potash alum, which I nowseparate from the mother-liquor, and I have found this alum to be achemically-pure article, not to be distinguished from the regulararticle of commerce produced in the usual way. The mother-liquor nowcontains the magnesia, iron, and manganese and the remaining aluminasulfate. This I concentrate again to a thick syrup and allow to coolslowly, when the alumina sulfate crystallizes out and I transfer it to apress and press out the mother-liquor again. The alumina sulfate in thisform I find to be identical with the alum cake of commerce, but not aschemically pure anarticle as the first portion of the alumina obtainedas potash alum. In this manner I obtain two grades of aluminasu1fate-one chemicwfiwflamq the other less pure, (alum'cake) The finalresidual liquor consists of a mixture of iron and manganese sulfates andchlorids, together with some magnesia sulfate. This I evaporate todryness and then calcine in a calcining-furnace with access of freeoxygen,which oxidizes the mixed sulfates to oxids "i igg ana ticle veryuseful asa're pigment and similar fifclfifia'cteTto the Venetian red ofthe arts.

What- I claim-as new and useful, and for which I desire Letters Patent,is as follows:

1. The process of treating furnace slag or cinder, which consists inmixing together about equal weights of such slag or cinder and sulfuricacid, together with five to twenty-five per cent. of the slag weight oflime, and separating the resultant lime sulfate and silica from thesoluble sulfates, substantially as specified.

2. The process of treating furnace slags or cinders, which consists insubjecting a mixture'of such slags or cinders and a regulated quantityof lime to the action of sulfuric acid and separating the resultantinsoluble lime sulfate and silica from the soluble sulfates,substantially as specified.

3. The process of treating furnace slags or cinders, which consists inmixing such slags with a regulated quantity of lime of about five totwenty-five per cent, and about an equal weight of sulfuric acid,separating the insoluble from the soluble portions, and recovering themagnesia contained in the waste liquor by concentrating the latter untilthe magnesia lime salt crystallizes out, and subsequently separatingthis from the residual liquor, substantially as specified.

4. The process of treating furnace slag or cinder, which consists inmixing such slag in a granulated form with about five to twentyfive percent. of lime, treating the mixture with about one to one and one-halfparts of sulfuric acid, separating the insoluble white residue from thesoluble sulfates, recovering the crystallizable magnesia sulfatecontained in the liquor as double sulfate of lime and magnesia, andrecovering the alumina as potash alum and alum cake by adding to theresidual liquor potassium salts and.crystallizing the alum and the alumcake, substantially as specified.

5. The process of treating furnace-slags, which consists in mixing suchgranulated slags with five to twenty-five per cent. of lime, treatingthe mixture with one to one and onehalf parts of sulfuric acid,separating the resultant white residue, recovering the crystallizablemagnesia sulfate as double sulfate of lime and magnesia, recovering thealu mina by adding to the residual liquor potassium salts, andcrystallizing out the alum, and recovering the residual iron, manganeseand magnesia by evaporating the final mother-liquor to dryness andcalcining the dry mixed sulfates and chlorids until they turn to oxids,substantially as specified.

6. The process of treating furnace slag or cinder, which consists inmixing the slag with about an equal weight of sulfuric acid, separatingout and recovering the resultant white Y residue of artificial gypsum,concentrating the residual liquor, and recovering the crystallizablemagnesia sulfate therefrom, adding to the second residual liquorpotassium salt, and recovering the crystallizable alumina sulfate asalum, concentrating again the third residual liquor, and separating theremainder of the alumina sulfate from the final residual liquor, andrecovering the iron, manganese and the balance of the magnesia byevaporating the final residual liquor, and drying and calcining thesolid products obtained therefrom, substantially as specified.

7. The process of treating furnace-slags, which consists in firstgranulating the same, and mixing therewith sufficient lime to bring upthe total percentage of lime to a constant, and second, adding sulfuricacid to such mixture, and grinding until the lime and the sulfuric acidreact to form lime sulfate, substantiallyas specified.

8. The process of treating furnace slag, which consists in firstgranulating such slag, second, mixing the same with sulfuric acid andgrinding such mixture until the lime and the sulfuric acid react to formlime sulfate, third, drying such mixture to dehydrate any gelatinoussilica, fourth, again grinding such mixture, and finally adding water toleach out the soluble sulfates, substantiallyas specified.

9. The process of treating furnace -slag, which consists in firstgranulating such slag, second, intimately mixing the same with sulfuricacid, until the lime and the sulfuric acid react to form lime sulfate,third, drying such mixture to dehydrate any gelatinous silica, andfourth, leaching out the soluble sulfates from such mixture,substantially as specified.

10. The process of treating furnace slag, which consists in firstgranulatin g such slag, second, intimately mixing the same with sulfuricacid until the lime and the sulfuric acid react to form lime sulfate,third, leaching out the soluble sulfate from such mixture, and

separating the insoluble residue from the resulting solution, andfourth, crystallizing and separating from such solution magnesia sulfateas double sulfate of lime and magnesia, substantially as specified.

11. The process of treating furnace -slag, which consists in firstgranulating such slag, second, intimately mixing the same with sulfuricacid until the lime and the sulfuric acid react to form lime sulfate,third, leaching out the soluble sulfates from such mixture, andseparating the insoluble residue from the resulting solution, fourth,crystallizing and separating from such solution magnesia sulfate asdouble sulfate of lime and magnesia, and fifth, adding a potassium saltto the residual liquor, and crystallizing therefrom potash alum and alumcake, substantially as specified.

In testimony whereof I affix my signature in presence of two witnesses.

SAMUEL V. VAUGI-IEN.

Witnesses:

FRANK. J. JENKINS, WILLIAM VAREATT.

